We propose a functional MRI (fMRI) study to probe the timing and location of neuro-hormonal interaction following food ingestion in humans. The proposal presents an explorative fMRI project by developing in vivo methods to characterize brain activity during hypoglycemia induced by prolonged fasting. We will examine brain responses during a real-time transition from fasting hypoglycemia to normoglycemia attained by eating (i.e., by oral glucose intake), focusing on the hypothalamus and its associated neural circuits. In particular, this project underscores two novel dynamic imaging approaches for tracing the time course of brain-hormone interaction during the transition. These approaches, namely (1) temporal clustering analysis (TCA) and (2) within-condition interregional covariance analysis (WICA), are critical to the timing of neuronal events that are interacting with hormonal processes, such as glucose-insulin regulation. Modeling of both temporal and spatial information about brain-hormone interaction will be our first step toward establishing a functional marker of hypoglycemia unawareness. By the functional marker we mean noninvasively -measured neuroendocrinal signals in response to a physiological challenge, such as fasting or eating. We hypothesize that alteration of such signals is implicated in the development of hypoglycemia unawareness, as in insulin-dependent diabetes mellitus (IDDM) accompanied by recurrent hypoglycemia. Although the ultimate goal of this project is to directly test this hypothesis in patient population under long-term intensive insulin treatment, which may require large-scale clinical trials, the current R21 proposal aims to develop new fMRI methodology involving a small number of subjects imaged under well-controlled conditions. While functional imaging methods may reflect a departure from traditional, symptom-dependent assessment of hypoglycemia unawareness (e.g., cognitive task testing or objective neurophysiological evaluation), it is still important to correlate fMRI analyses with routine clinical measurements, such as counterregulatory hormone levels by blood sampling. This correlation may provide information for delineating the neural bases about how internal biochemical signals give rise to the awareness of hunger or satiation, and for understanding the phenomenon of hypoglycemia unawareness. Two specific aims are to be accomplished in this two-year project: Aim 1. Development of a fasting-eating fMRI paradigm by correlating functional imaging signal with biochemical measurement; and Aim 2. Development of both temporal and spatial reference systems for the in vivo modeling of glycemia regulation and hypoglycemia unawareness.